Material Comparison

I am trying to read the forum and determine the best type of material to repair a boat I have recently purchased, but am not really getting answers to my questions and hope someone can help.

I have never worked on a fiberglass boat and thought epoxy was the final word, but I see that most FG boats have a gel coat. So, is that polyester? What is the advantage of polyester over epoxy? And, what about paint? It looks like I am going to have to do quite a bit of filling sanding to get the hull fair and smooth.

Can I just sand/fill and then roll on Poly? Is that a gel coat? Should I have it sprayed? Is that cost effective? My wife is not happy about the boat, but is being very accommodating.....

Paint? Is there a top coat if I paint? What protects it from the ocean and my trailer?

Epoxy? Is that an option? I haven't seen anyone talk about epoxying the hull as an outer coat.

I haven't seen a dedicated discussion that lays out the positives and negatives and the must not do's, e.g don't put poly on epoxy.

Am I leaving out any options?

Best Regards,

Johnny

 

This forum, if searched, could distill into a hundred books about epoxy vs/and polyester resins, but nothing here takes you by the hand and guides you through each step.
Use the search feature.
You will need a bit of reading material. There are a lot of books out there dealing with basics of fg boat repair.
Before doing anything, like sanding or grinding, stop and dewax the area with some acetone, scrubbing with an abrasive sponge (in case you are already getting started).
Read a bit first. This isn't the place for basic reading but it will fill in and answer your questions. A good repair book will generate a lot of questions regarding details. Those would be answered here (by all means ask away right now, but realize there's so much to know, no one is going to be able to help you much until you do some homework.
Looks like you've got some blistering below the waterline.

 

Alan,

I've gone through, searched the site, and read about eaxh technique. I was hoping for more of a compare/contast the different materials that are available as an outer coat.

PS- did I mention I am in Iraq and can not get to a library? Reading material is soley from the intenet at this point.

Thanks!

Johnny

 

I think youi have osmotic damage. The first thing to do is to see how extensive the damage is. What's showing isn't necessarily the full extent of the blistering. You will have to look for bumps-- they can be best seen with a lightg askance of the hull. Unless you pick out (with a pick) all of them, you shouldn't waste time sealing the hull, which should be done with an epoxy barrier coat.
This is how epoxy and polyester differ. Polyester allowed water to get into the fiberglass, slowly over time. It reacted with the component parts of the poly resin and expanded, creating a lot of blisters that popped and left tiny craters. The whole below-waterline hull should be ground down to the glass (removing the gel coat) and built back up with epoxy resin, faired, and painted with a polyurethane paint. It's a ;lot of work, and you should be prpared to spend hundreds and a lot of hours doing work that's not fun at all.
The gouge in the forefoot is nothing in comparison.

 

Yep, there isn't a step by step, which seems to be what you're looking for. The reason is simple, there are way too many variables for this.

'Glass repairs can be fairly basic in nature. It boils down to accessing the damage, repair needs, grinding out what needs grinding (or sanding), applying a skim coat, reinforcement etc. as the particular area demands (each is different) then top coating to protect from the elements.

You have several different issues. The gel coat is worn out in spots, you also appear to have some stress cracks and possibly some impact damage.

Gel coat is the pigmented, resin rich top coat that is applied in the manufacture of your boat. It's a polyester and used because it's cheap, self releasing and fairly easy to control. Is it the best thing, probably not, but it suits manufacturing needs. Trying to apply more gel coat as a novice, with backyard methods and shade tree tools means it'll never be a very good job. So, you're left with painting to get a nice finish.

Epoxy is what I recommend for repairs like yours, particularly for a beginner. It's easier to work with, less sensitive to screw ups and much stronger then poly.

In the areas where the gel coat is worm off, but the hull in fairly good shape, you just need to apply a building epoxy primer, smooth this, then a paint to finish it off.

The stress cracks should be cleaned out, maybe opened up a little to get back to solid mat, filled with thickened epoxy, then sanded smooth. After this, seal the area with epoxy, then prime and paint.

The damaged areas need to have the damage ground out, back to good, solid mat. The material removed replaced with epoxy, fabric and fillers to restore the integrity of the area, then continue on with priming and paint.

Each of these things are cover many times here in previous posts. Yep, it's a lot of reading, but eventually you'll get an idea of how things work.

 

PAR and Alan,

I don't think I was stating my question succinctly, since you both read it the same way. However, fromm your replies, I have been able to do some more digging and found my answer.

I was looking more to the why each particular material is used, not so much the how. Poly is cheaper, more porous and more difficult do apply correctly. Epoxy is more expensive but a better sealer- and easier to work. Marine paint on epoxy.

Thanks for all the help! Now, if I can just get the wife to work a sander....

johnny

 

It's actually simple economics 101. Lets say it costs 30% more to use a better resin system, per yacht. This means you neighbor yacht building buddy can under cut you at the same profit margin and he'll have the better tee times on Saturday morning.

Some manufactures and many custom or semi custom builders have moved to the better resin systems, but it's still the ageless debate, "quantity or quality". Do you build less well or a bunch at lower cost. Wal-Mart has shown which is a more profitable approach. This doesn't mean you have to live with it when it's time for repairs though . . .

 

PAR,

thanks again for sharing your knowledge. So, I have pretty much decided that I want to go with epoxy. Seems the only advantage to poly is the glossy shine it gives.

So, one last question; What is blush? I know what it looks like and what I should do to make sure my layers adhere- but, is it chemically, a soap or oil maybe?

Cheers,

Johnny

 

OK- I found what I was looking for. I hope it's ok, but I nicked it off the epoxymethods.com website. After reading this, I wonder why anyone would use poly, except maybe to patch?

The Resin Families: Epoxies, Vinylesters and Polyesters

Epoxies, polyesters and vinylesters represent two resin families. Epoxies belong to a family of resins, which are epoxy functional, which can be cured with amine curing agents at room temperatures to form excellent adhesives and composite resins. Polyesters and vinylesters belong to a family of resins containing an unsaturated polyester or hybridized vinylester backbone which is catalyzed with a peroxide (normally Conap and MEKP) to condense into a cross-linked solid resin.

RESINS AND ADHESIVES

Resins (liquid plastics, i.e. epoxies, polyesters and vinylesters) are commonly used by the marine industry when wetting out fiber reinforcing in order to saturate the fibers and form an FRP (fiber reinforced plastic) part. Whether the part utilizes fiberglass fibers, carbon fiber, Kevlar aramid, or wood fibers adhesions to and wetting of the fibers is a critical step in the production of a quality part.

EPOXIES

Epoxies represent some of the most versatile resins available to the composite manufacturer and marine repairer. Generally in all categories, the builder/repairer will realize the greatest degree of bond strength, and toughness with well formulated epoxies. New generation MAS Epoxies are VOC free and have curing systems which are phenol free (representing a safe step forward for all resin users). Atmospheric moisture is of little concern as blush free MAS systems allow the builders and repairers to laminate with little or no preparation between applications as long as mix ratios are followed and mixing is adequate. Shrinkage of MAS epoxies is below .03% eliminating prerelease. In the case where a part, originally manufactured utilizing polyester or vinylester, has yielded to strain and cracked, a well-reinforced epoxy repair will tenaciously hold to the substrate with 2000-psi (vinylester 500 psi). Many high strain repair areas and lightweight parts must flex and strain without micro fracturing. MAS resins have the ability to strain with the fibers while maintaining permanence and adhesion. Whether a part or repair is made of wood, carbon, Kevlar, fiberglass, core material or hybrids of the above, MAS Epoxies will wet and permanently stick with and to the composite. Just as a quick note, one composite manufacturer recently eliminated a peroxide cured extremely pricey custom formulated aerospace adhesive (fancy packaging and all) with a standard MAS product. The benefits included an elimination of VOC's from the assembly area, reduced price, increased strength, and elimination of shrink problems from the bond line. When MAS Epoxies are used for a chemical resistant barrier (barrier coating) the finished coating system has excellent resistance to water uptake (below .5%) and the applicator can be confident that subsequent finishes will stick to the new epoxy and the epoxy will stick with the hull. New generation epoxies feature many of the advantages of low viscosity and accurately tailored gel and cure times. Permanent repairs and the highest quality custom aerospace construction have been enjoying the advantages of epoxies since the sixties. MAS brings these advantages the builder and repairer at room temperatures in the nineties and are gearing up more surprises for 2000 and beyond.

VINYLESTER

Vinylesters represent a resin development step in the right direction. While still utilizing a polyester resin type of cross-linking (i.e. peroxide cured). These hybrid resins are toughened with epoxy molecules within the backbone. Shrinkage is less of a concern with vinylesters and prerelease of the part from the mold is reduced. The toughening effect of the resin modifications makes for a better resistance to micro fracturing and some of the secondary functionality of the backbone assists in adhesion to substrates. Vinylesters are capable of forming secondary bonds around 500 PSI (MAS Epoxies 2000 PSI). Resistance of vinylester resin to moisture is good and some commercial barrier coatings have been marketed utilizing this resin family. The down side of the vinylesters include sensitivity to mixing, handling, high VOC's (in the form of styrene), atmospheric moisture and temperature sensitivity (sometimes it just will not cure). Good tough vinylester is also quite pricey when compared to polyesters, in fact the dollars per pound approach that of epoxies. Vinylesters definitely represent an improvement over polyesters when considering standard peroxide curing, however adhesion to dissimilar and already cured substrates is still far below perfect and many vinylester hulls suffer similar massive delamination of the hull skins from core and bulkhead substrates. Additionally since almost all barrier-coating applications are after market it is essential that the coating system have maximal bonding strength to the original substrate. Vinylester resins only show good fiber adhesion to standard glass fiber, standard low adhesions to more exotic fibers (Kevlar/carbon fiber) and wood.

Open surface curing of both vinylesters and polyesters requires a surfacing agent. Subsequent applications require careful surface preparation if reasonable adhesion is to be achieved.

POLYESTER

Polyesters are one of the least expensive resins available to the FRP boat builder utilizing female tooling in the form of a mold. Polyester has the advantage of being extremely inexpensive when compared with other thermoset resins i.e. vinylesters and epoxies. If the upside is cheap pricing, the down side includes poor adhesions, high water absorption, high shrinkage, and high VOC's. Polyester resins are only compatible with fiberglass fibers. Polyester is best suited for applications insensitive to weight and do not require high adhesion or fracture toughness. For instance if a simple inexpensive solid fiberglass part must be fabricated in open tooling in one operation and requires no secondary bonding. If shape accuracy is not critical, resistance to water is of no concern, and ventilation of the workspace is excellent, then polyester's a great candidate. Polyesters historically exhibit poor performance in the areas of adhesion and elongation, rendering the finished part prone to micro cracking and secondary bond failures. These parameters become more important when we consider adhering dissimilar materials within the same part or welding any materials that are not the usual fiberglass strand substrate. Finished polyester hulls are still suffering from osmotic blistering when untreated by an epoxy barrier coating against water. Boat yards are filled with hull and superstructures suffering from massive areas of core disbonding or delamination resulting from an adhesive mismatch with the industry at large (i.e. depending on polyester as an adhesive).

 

Go here:

http://www.yachtsurvey.com/Fiberglass_Boats.htm

and have some very interesting thoughts about fiberglass boats, composite building and foam cores.
Notice that this is NOT the bible of boat survey, there are several points one could contradict the author, but it gives a general overview of (especially poly related) issues.